1. Field of the Invention
The present invention relates to a nitride-based semiconductor. In particular, the present invention relates to a fabrication method of nitride-based semiconductors capable of forming a nanoscale uneven structure on a sapphire substrate to decrease the stress and resultant dislocation between the sapphire substrate and a nitride-based semiconductor layer while increasing the quantum efficiency between the same. The invention also relates to a nitride-based semiconductor fabricated according to the above fabrication method of nitride-based semiconductors.
2. Description of the Related Art
A Light Emitting Diode (LED) basically consists of a junction of p- and n-doped semiconductor layers formed on a sapphire substrate as a kind of optoelectric device. When applied with electric current, the electron-hole combination in the LED converts energy corresponding to its band gap into light.
The semiconductor layers of the LED a re obtained by growing Gallium Nitride (GaN) single crystalline thin films on a heterogeneous substrate of sapphire, SiC, oxide or carbide via Metal-Organic Chemical Vapor Deposition (MOCVD) or Molecular Beam Epitaxy (MBE). However, because the substrate material such as sapphire is not identical with GaN in lattice constant and thermal expansion coefficient, high quality nitride single crystal is hardly grown on the substrate.
Two stage heteroepitaxy using a low temperature nucleation layer is adopted in order to solve this problem. However, a nitride layer grown in this solution contains crystal defects up to about 109 to 1010 cm−2.
Crystal defects deteriorate properties of resultant nitride-based semiconductors. Thus, several techniques such as Epitaxial Lateral Overgrowth (ELOG) are developed in order to reduce the crystal defects. A patterned substrate is also used to solve this problem.
However, these techniques have drawbacks in that excessive efforts are needed for the growth of LEDs since lateral growth takes a long time. Also, another problem is observed that crystal defect density is low only in wing regions.
Furthermore, because a substrate is patterned with a microscale-patterned mask, the pattern size of the substrate cannot be made smaller than the magnitude of the mask pattern. That is, when formed on substrates, patterns by conventional method are sized larger than a predetermined value, which in turn maintain crystal defect density at predetermined levels or more.